The regulation of triacylglycerol, phosphatidylcholine, and phosphatidylethanolamine biosynthesis will be investigated by enzymological studies of individual enzyme activities in microsomal preparations. The studies will employ isolated rat fat cells, liver, and 3T3-L1, a "preadipocyte" cell line. The specific objectives include studies designed to substantiate the conclusion that triacylglycerol, phosphatidylcholine and phosphatidylethanolamine biosynthesis occurs on the cytoplasmic surface of microsomal vesicles. A determination of whether molecules like glycerol-P, CDP-choline and CDP-ethanolamine penetrate the microsomal membrane will be made. Attempts to localize the newly synthesized lipid products are proposed. In addition, studies in isolated fat cells will determine whether the glycerol-P acyltransferase is acutely regulated. Changes in triacylglycerol biosynthetic activities during the adipose conversion of 3T3-L1 cells will be further investigated by examining the role of insulin, enzyme turnover, and possible short-term regulation.